The present invention relates generally to aircraft de-icing operations and more particularly to apparatus that mix and dispense deicing liquids that are in turn sprayed onto aircraft.
In northern climates during winter months, aircraft which are either parked on the ground overnight or which are on the ground during severe winter weather frequently accumulate snow or ice on the airfoil surfaces. It is thus necessary to remove this material prior to takeoff and such removal has been the subject of a variety of deicing equipment in the prior art. The typical approach is to apply deicing compositions to aircraft in wintery weather before takeoff to deice them and to prevent ice from forming for a certain period (the so-called xe2x80x9chold-over timexe2x80x9d). This goal is frequently achieved with mixtures of water and ethylene glycol or water and propylene glycol.
The most popular equipment to apply the deicing mixtures are self-contained trucks having an extendible and maneuverable boom mounted thereon and a tank containing the deicing mixture. The truck typically includes a self-contained heater that heats the glycol-water mixture to 160 to 190 degrees Fahrenheit. The heated deicing fluid is then pumped through a hose to the end of the boom where the operator directs a stream of the heated deicing fluid mixture from a nozzle onto the aircraft. This procedure removes the snow and/or ice and provides a coating of glycol which largely prevents further formation of the freezing substance during the hold-over time. This deicing procedure normally takes place on the tarmac just prior to the plane""s departure after which the aircraft""s normal internal electrical deicing systems are employed.
It is known to provide xe2x80x9cglycol proportioning panels,xe2x80x9d as they are known in the art, that mix water and pure ethylene or propylene glycol and provide the mixture to the trucks that in turn spray it onto the aircraft. Most of these known proportioning panels are large, ungainly, expensive and offer limited mixing functionality.
For example, one disadvantage of these known proportioning systems is that the desired ratio of glycol to water is typically limited to only three or four settings. However, to minimize glycol waste and to optimize the mixture for a given weather condition, more selections of glycol mixtures are desirable. Another disadvantage to presently available glycol proportioning panels is that the systems are housed in a building that may be hundreds of feet from where the truck that sprays the mix onto the aircraft is loaded. The mixture is piped over this distance. The distance between the main unit and the location where the effluent is being dispensed can create a communication problem between the operator of the panel who is located in the building, and the personnel who are loading the truck, who are outside and several hundred feet away.
Another disadvantage of known proportioning systems is that they employ variable speed or frequency pumps to proportion the percentages of glycol and water. In addition to creating more process variables to be monitored, the variable speed pumps can be undesirably slow.
Systems relying on multiport computer controlled valves to mix glycol and water are also known. For example, U.S. Pat. No. 4,842,005 (Hope et al.) discloses a glycol proportioning station wherein water is pumped by a pump and its flow rate measured by a flow meter. Glycol is pumped through another pump and through a multi-port valve, which has multiple ports of different sizes that are pneumatically opened or closed in response to pre-programmed signals from a controller that is coupled to the multiport valve. In use, the water flow rate is sensed and the flow of glycol is controlled by the multi-port digital valve, which opens and closes any number of ten possible elements, or parts, to accommodate the required flow.
It is also known in the art to use refractometers with glycol mixing systems for aircraft. For example, U.S. Pat. No. 4,986,497 to Susko discloses a deicing system in which a refractometer is used to monitor the mixed fluid and adjust flow of the glycol and water lines as necessary. Separate supply lines provide controlled flows of water and glycol to a wye-connection point. Each supply line has its own pump and throttling valve to control flow, as directed by a microprocessor. The system includes a heat exchanger into which fluid is recycled until the glycol mix reaches the desired temperature and until the refractive index read by a refractometer has reached the set point. The refractometer output signal indicates whether the refractive index is at, below, or above the set point. If below the set point, the microprocessor adjusts a valve on the glycol line to add glycol to the mix; if above the set point the microprocessor adjusts the valve on the water line to add water to the mix. Once the correct temperature and refractive index are recognized at the microprocessor, a valve is opened on the effluent line and the mixture is delivered.
U.S. Pat. No. 4,275,593 (Thornton-Trump) discloses an aircraft deicing system which includes a specific gravity meter that displays the glycol percentage to an operator positioned in a basket and a lever to adjust the glycol percentage in the effluent. By adjusting the lever, the operator may vary the amount of pure glycol fed into the mixture line and thereby adjust the glycol percentage in the effluent.
In summary, known glycol proportioning panels can be expensive, slow and inflexible. What is needed is a glycol proportioning panel that addresses these drawbacks.
The present invention provides a glycol proportioning station that provides a deicing mixture of glycol and water to tank trucks that in turn spray the deicing mixture onto aircraft. The invention includes two independent ways to modulate flow in the separate glycol and water lines that are merged into the effluent. The first method involves measuring the flow rates in the individual glycol and water lines, totalizing them and calculating the percentage of glycol in the effluent. The second method involves reading the refractive index of the effluent and converting it to glycol concentration.
The system""s refractometer can thus be used as a back-up to check the glycol concentration of the effluent, and a visual or audible warning signal can be activated when the percentage of glycol in the effluent, as read by the refractometer, is outside of the set tolerance, typically about two (2) percent. In another form of the present invention, the refractometer can be used in a feedback loop which includes a microprocessor to adjust flow control valves instead adjusting them based upon the flow meters. In another preferred form, the flow can be initially set by adjusting one or more characterized ball valves on one or more of the glycol or water input lines. Then, after flow has reached substantially steady state, flow can be modulated by means of the refractometer feedback loop just discussed.
In another embodiment of the present invention, a remote control is positioned where the truck is loaded and runs in parallel with the controls on the main unit of the system. The main unit includes a first control panel having a first display mounted thereon for controlling the operation of the proportioning station. A remote control panel having a second display is located a distance from the main unit, and is capable of operating the main unit in parallel with the controls on the main unit.
In another form thereof, the present invention provides a method of obtaining a desired mixture of glycol and water for use in deicing aircraft. The method comprises providing two input lines, one adapted to transport glycol and the other adapted to transport water, and merging the lines into an effluent line. Substantially constant flow of glycol and water is provided to the two input lines, respectively. Preferably, the flow rates are matched by adjusting a pressure reducing valve on the line which has the greater maximum flow. The flow rates in the two input lines are monitored and glycol percentage in the effluent is calculated therefrom. The refractive index of the effluent is monitored with a refractometer and converted into glycol concentration. The glycol concentration measured from the refractometer is compared to the calculated percentage of glycol. Finally, if the glycol concentration measured from the refractometer is outside a predetermined tolerance, either an error signal is produced or the system uemploys a feedback loop to adjust one of the flow control valves.
One advantage of the present invention is that it provides an accurate yet reliable system for proportioning a mixture of water and glycol. Advantageously, the system includes two separate means for determining glycol concentration. The system""s on-line refractometer can be used to verify the accuracy of the glycol percentage calculated by measuring the individual flow rates of glycol and water, or it can be used as an independent means for modulating glycol or water flow. The system also provides the capability of initially mixing based upon flow rates then later mixing based upon the refractometer reading.
Another advantage of the present invention is that the proportioning station can be controlled proximate the tank truck which will spray the mix on the aircraft. This avoids communication problems between the operator of the station and the operator filling the truck, and thereby makes it easier to accomplish the job. The remote panel may also allow the dispensing of the glycol mix to be accomplished with one less person.
Another advantage of the present invention is that it uses substantially constant flow, which allows a much quicker fill time. Flow rates up to 300 gallons per minute or more are possible, which is much faster than systems employing variable frequency pumps.
Yet another advantage of the present invention is that it is economical. Glycol stations employing the present invention may cost only a fraction of the cost of competing glycol proportioning stations, which can ultimately help reduce the cost of air travel.
Still another advantage of the present invention is that it provides a uniform mixture of glycol and water with an economy of moving parts. This is accomplished by building a static mixer into the effluent line downstream of the manifold which merges the glycol and water streams. The static mixer provides uniform mixing under very low temperatures or if thickening agents are added to the glycol.